Polycrystalline diamond (PCD) materials known in the art are formed from diamond grains or crystals and a ductile metal catalyst/binder, and are synthesized by high temperature/high pressure processes. Such PCD materials are well known for their mechanical property of high wear resistance, making them a popular material choice for use in such industrial applications as cutting tools for machining, and subterranean mining and drilling, where the mechanical property of wear resistance is highly desired. In such applications, conventional PCD materials can be provided in the form of a surface coating on, e.g., inserts used with cutting and drilling tools, to impart improved wear resistance thereto. Traditionally, PCD inserts used in such applications are formed by coating a suitable substrate material with one or more layers of PCD-based material. Such inserts comprise a substrate, a PCD surface layer, and often one or more transition layers to improve the bonding between the exposed PCD surface layer and the underlying substrate support layer. Substrates used in such insert applications are preferably formed from a carbide material, e.g., tungsten carbide (WC) cemented with cobalt (WC—Co).
The coated layer or layers of PCD conventionally may comprise a metal binder up to about 10 percent by volume. The metal binder is used to facilitate intercrystalline bonding between diamond grains, and acts to bond the layers to each other and to the underlying substrate. Metals conventionally employed as the binder are often selected from the group including cobalt, iron, or nickel and/or mixtures or alloys thereof. The binder material can also include metals such as manganese, tantalum, chromium and/or mixtures or alloys thereof. The metal binder can be provided in powder form as an ingredient for forming the PCD material, or can be drawn into the PCD material from the substrate material during the high temperature/high pressure processing.
The amount of binder material that is used to form PCD materials represents a compromise between the desired material properties of toughness and hardness/wear resistance. While a higher metal binder content typically increases the toughness of a resulting PCD material, higher metal content also decreases the PCD material hardness and corresponding wear resistance. Thus, these inversely affected desired properties ultimately limit the flexibility of being able to provide PCD coatings having desired levels of both wear resistance and toughness to meet the service demands of particular applications. Additionally, when variables are selected to increase the wear resistance of the PCD material, typically brittleness also increases, thereby reducing the toughness of the PCD material.
Conventional PCD materials comprise a large amount of fine-sized diamond grains or powder. Fine-sized diamond grains are intentionally used as a raw material for making conventional PCD materials to increase the volume fraction of diamond in the PCD material, which increases the wear resistance of the sintered PCD material. Conventional PCD materials can either be formed exclusively from fine-sized diamond grains, or can be formed from a mixture of fine-sized diamond grains with coarse-sized diamond grains. In either case, however, such conventional PCD materials rely on the intentional use of a defined proportion of fine-sized diamond grains to increase the hardness and overall wear resistance of the PCD material.
Generally, such conventional PCD materials exhibit properties of extremely high hardness, high modulus, and high compressive strength, and provide a high degree of wear protection to a cutting or drilling element. However, in more complex wear environments known to cause impact and high-load fatigue, layers formed from such conventional PCD materials are known to fail by gross chipping and spalling. For example, drilling inserts coated with a conventional PCD layer can exhibit brittleness that causes substantial problems in practical applications. The breakage and/or failure of conventional PCD materials in such applications is a result of the relatively low toughness of the material.
It is, therefore, desirable that PCD materials be developed that display improved properties of impact and fatigue resistance and functional toughness for use in complex wear environments, when compared to conventional PCD materials, while displaying acceptable wear resistance for use in the same applications.